1. Field
A method of manufacturing a centrifugal fan is disclosed.
2. Background
A centrifugal fan is a fan that accelerates air introduced in an axial direction through a shroud and discharges the air in a radial direction through gaps between blades. Such a centrifugal fan may be formed of a synthetic resin or metal. A resin centrifugal fan advantageously permits manufacture of blades having various shapes via injection molding, but has poor strength. Therefore, centrifugal fans to be applied to large products are appropriately formed of a metal.
Conventionally, a metal centrifugal fan is manufactured by cutting a metal sheet in a given shape, bending the metal sheet to define a positive pressure surface portion and a negative pressure surface portion, and thereafter, bonding the positive pressure surface portion and the negative pressure surface portion to each other. For example, Japanese Patent Laid-open Publication No. 2000-45997 discloses a blade formed by bending a single metal sheet. In the above patent, the blade formed by bending a single metal sheet has an airfoil cross section. More particularly, the blade has a three dimensional shape in which a leading edge of the blade has a predetermined inclination relative to a rotational axis of a centrifugal fan and a trailing edge of the blade is parallel to the rotational axis. However, as exemplarily shown in the above patent, respective, airfoil cross sections of the blade taken at arbitrary layers perpendicular to the rotational axis have a common camber line. For example, although a lower edge of the blade bonded to a main plate has a longest camber line and an upper edge of the blade coming into contact with a shroud has a shortest camber line, the camber line at the upper edge completely overlaps the camber line at the lower edge. The blade having the above-described shape is an inevitable consequence of bending a single metal sheet using a mold that defines a single camber line as exemplarily shown in the above patent.
As described above, although Japanese Patent Laid-open Publication No. 2000-045997 discloses the metal blade, the blade has a limit in terms of shape, thus having difficulty in having a complicated three dimensional shape, such as, for example, a shape in which a camber line of an airfoil taken at an upper cross section of the blade and a camber line of an airfoil taken at a lower cross section of the blade cross each other, in other words, a twisted shape in a rotational axis.
It is one object to provide a method of manufacturing a centrifugal fan capable of providing more diversified shapes of a positive pressure surface or a negative pressure surface.
It is another object to provide a method of manufacturing a centrifugal fan having a blade comprised of two metal members.
It is another object to provide a method of manufacturing a centrifugal fan having a blade of a complicated three dimensional shape that has not been easily achieved using a metal in the related art.
It is another object to provide a method of manufacturing a centrifugal fan capable of achieving reduced material cost and enhanced rigidity.
It is another object to provide a method of manufacturing a centrifugal fan capable of being applied to larger products than in the related art.
It is another object to provide a method of manufacturing a centrifugal fan having a blade in which a positive pressure surface and a negative pressure surface are curved surfaces having different curvature variations.
It is another object to provide a method of manufacturing a centrifugal fan capable of achieving reduced flow resistance, more particularly, enhanced efficiency via improvement in the shape of a blade.
It is another object to provide a method of manufacturing a centrifugal fan capable of allowing a blade having a three dimensional shape to be easily coupled to a shroud or a main plate.
It is a further object to provide a method of manufacturing a centrifugal fan capable of minimizing welding beads between members, thereby restricting increase in flow resistance and minimizing a negative effect on balancing of the fan due to the welding beads.
In accordance with one embodiment, the above and other objects can be accomplished by the provision of a method of manufacturing a centrifugal fan, the method including the steps of: (a) cutting a metal sheet to form a positive pressure surface forming member and a negative pressure surface forming member respectively configuring a positive pressure surface and a negative pressure surface; (b) pressing the positive pressure surface forming member and the negative pressure surface forming member to form a first curved surface portion configuring the positive pressure surface and a second curved surface portion configuring the negative pressure surface; (c) trimming the positive pressure surface forming member provided with the first curved surface portion and the negative pressure surface forming member provided with the second curved surface portion to form a shroud bonding surface portion and a main plate bonding surface portion; (d) bending the shroud bonding surface portion and the main plate bonding surface portion; (e) bonding the positive pressure surface forming member and the negative pressure surface forming member to each other; and (f) bonding the shroud bonding surface portion and a shroud to each other and bonding the main plate bonding surface portion and a main plate to each other in a bonded state of the positive pressure surface forming member and the negative pressure surface firming member.
The first curved surface portion and the second curved surface portion may define different shapes of curved surfaces.
In the step (c), trimming may be implemented such that an upper edge and a lower edge of each of the positive pressure surface forming member and the negative pressure surface forming member are bent independently of a front edge of each forming member in the step (d). The step (e) may include bonding front edges of the respective forming members to each other and bonding rear edges of the respective forming members to each other. At least one of bonding between the front edges of the respective forming members and bonding between the rear edges of respective forming members may be implemented by resistance welding. The resistance welding may be implemented at a plurality of positions aligned in a line from the shroud to the main plate in a state in which the front edges or the rear edges of the respective forming members come into contact with each other. The resistance welding may be spot welding.
The resistance welding may be projection welding, and the method further include the step of forming protrusions at any one of the positive pressure surface forming member and the negative pressure surface forming member so as to protrude toward the other one. The protrusion forming step may include forming the protrusions at a plurality of positions, aligned in a line from the shroud to the main plate, on at least one of the front edge and the rear edge of any one of the positive pressure surface forming member and the negative pressure surface forming member. The step (e) may include simultaneously melting the protrusions.
The method may further include the step of processing a rivet hole in at least one of the shroud bonding surface portion and the main plate bonding surface portion, and the step (f) may include fastening a rivet through the rivet hole to couple at least one of the shroud bonding surface portion and the main plate bonding surface portion to the shroud or the main plate. The step (f) may include bonding each of the shroud bonding surface portion and the main plate bonding surface portion to the shroud or the main plate in a fastened state of the rivet. Bonding between the shroud bonding surface portion and the shroud or bonding between the main plate bonding surface portion and the main plate may be implemented by resistance welding. The resistance welding may be spot welding implemented at a plurality of positions aligned in a line from the front edge to the rear edge of each forming member.
The method may further include the step of repeatedly implementing the step (b) after the step (d).
According to embodiments, a method of manufacturing a centrifugal fan has the effects of achieving higher rigidity than that of a conventional centrifugal fan formed of a resin material and of enhancing performance of the fan owing to a three dimensional shape of blades.
In addition, as a result of processing two thin metal sheets respectively and bonding the same to each other, the present invention has the effect of enabling formation of a blade having a complicated three dimensional shape that has not been easily achieved in the related art.
In addition, the blade comprised of the two sheets, moreover, has the effect of achieving less material cost, higher efficiency of the fan owing to weight reduction and reduced power consumption than in the related art.
In addition, since two members are first processed as curved members respectively and then bonded to each other to construct a blade, the members have independent shapes of curved surfaces, which has the effect of enabling formation of a blade having a complicated three dimensional shape (for example, a positive pressure surface and a negative pressure surface of the blade are curved surfaces having different curvature variations).
In addition, the metal blade having a complicated shape has the effect of reducing flow resistance and enhancing performance of the fan, more particularly, efficiency of the fan.
In addition, the embodiments has the effect of easily coupling the blade having a three dimensional surface to a shroud or a main plate.
In addition, welding beads between members may be minimized, which has the effect of restricting increase in flow resistance and minimizing a negative effect on balancing of the fan due to the welding heads.
In addition, no bonding portion or coupling portion between constituent members of the blade is present at the positive pressure surface or the negative pressure surface, which has the effect of reducing flow resistance.
In addition, embodiments has the effect of achieving increased strength and reduced ductility due to characteristics of plastic working.